Engines that are built into the main libcrypto OpenSSL library can't be
disabled through UCI. Add a 'builtin' setting to signal that the engine
can't be disabled through UCI, and show a message explaining this in
case buitin=1 and enabled=0.
Signed-off-by: Eneas U de Queiroz <cotequeiroz@gmail.com>
0b70d55a64